collier.] METHODS OF ASSAY. 43 
All ores must be crushed and carefully concentrated b}^ sizing and 
panning. For a prospector's field test of ore supposed to carry a small 
percentage of tin, a practical method would be to crush the supposed 
tin ore in a hand mortar and concentrate by panning, after which the 
concentrates can be roasted and cleaned with a magnet and the residue 
tested with a blowpipe, as has been described. 
As small globules of tin, such as are obtained by the blowpipe, are 
sometimes unsatisfactory, more metal can be reduced by simple means. 
While at Teller this seemed desirable, and an old teacup was lined one- 
fourth inch thick with a paste of powdered Wellington coal and baked. 
The finely pulverized ore was mixed with an equal bulk of powdered 
coal and twice as much ordinary baking soda; this charge was placed 
in the cup and covered one-half inch deep with powdered coal and 
heated for forty-five minutes in an ordinary cook stove with as hot a 
fire as possible. Although the cup broke upon attempting to remove 
it from the fire, *good-sized buttons of tin, as large as a pea, were 
obtained. After determining the presence and the relative value of 
the washed cassiterite, pan assays will be found sufficient for further 
tests. 
Greater accuracy in the assay of tin ores is obtained by wet analysis. 
Such analyses of eight samples of low-grade tin ores from the Seward 
Peninsula were recently made in the laboratory of the United States 
Geological Survey. These ore : contained no visible crystals of cassit- 
erite, and were treated without mechanical concentration. The fol- 
lowing note in regard to the wet method of analysis is furnished by 
Mr. Eugene C. Sullivan, of the United States Geological Survey: 
The method used in detecting traces of tin was as follows: Two grams were roasted 
in platinum crucible, fused with potassium bifluoride (KHF), and the melt was twice 
evaporated with concentrated sulphuric acid (H 2 S0 4 ) to insure absence of hydro- 
fluoric acid (HF). The mass was taken up with dilute sulphuric acid (H 2 S0 4 ), in 
which practically all dissolved. The solution was decanted from any slight residue, 
which was fused as before with potassium bifluoride (KHF) and after driving off 
hydrofluoric acid ( HF) by means of sulphuric acid ( H 2 S0 4 ) added to the main solution. 
The solution was nearly neutralized with ammonium hydroxide (NH 4 OH), and 
hydrogen sulphide ( H 2 S ) was passed through it for several hours. The precipitate was 
digested for some time with yellow ammonium sulphide, being warmed slightly. The 
insoluble residue was filtered out, the filtrate acidified slightly with sulphuric acid 
(H 2 S0 4 ), and hydrogen sulphide (H 2 S) was passed to insure complete precipitation 
of stannic sulphide (SnS 2 ). The precipitate was filtered out and ignited, again fused 
with potassium bifluoride (KHF), evaporated with concentrated sulphuric acid 
(H 2 S0 4 ), taken up with dilute sulphuric acid, stannic acid (H 2 Sn0 3 ) precipitated 
with ammonium hydroxide (NH 4 OH), the precipitate dissolved in hydrochloric acid, 
any residue filtered out, the solution neutralized with ammonium hydroxide (NH 4 OH) 
and hydrogen sulphide (H 2 S) passed for some hours. 
Where the tin was present a yellow precipitate of stannic sulphide (SnS 2 ) separated, 
apparent on allowing the solution to stand for some time. To obtain an idea of the 
amount of tin present this precipitate, after thorough washing, was ignited and 
weighed as stannic oxide (Sn0 2 ). 
